The present invention relates to digital printing. It finds particular application in conjunction with detecting color objects in a scanned image and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications.
An automated decision identifying whether a scanned image is neutral or contains color objects is important for further processing and printing. When correctly recognized as neutral, it may be desirable to render an image using merely black K toner, rather than toners used for printing colors and process neutrals (e.g., the cyan-magenta-yellow-black (“CMYK”) colorants), to potentially increase print quality. Using the CMYK colorants to render an image may decrease printing speed by as much as about four (4) times relative to rendering an image using merely black K toner. In some situations, however, it is desirable to render an original image using all four (4) of the colorants. For example, an image of black text may also include a small company logo or a single word and/or symbol emphasized in color (e.g., on an instruction sheet enclosed with medications). It is desirable to render such an image using all four (4) of the colorants.
Conventional methods for color detection are implemented by transforming the image into the CIELab color space. Then, the number of pixels within the image having a chroma above a suitable threshold are determined. If some other color space is preferred in the image processing path, suitable measures of pixel chroma and lightness must be developed before a general scheme of image processing, which may include isolating the legitimate color pixels, can be applied. In addition to the legitimate color pixels, undesirable color pixels, mostly at the edges of neutral areas may also be generated in the scanning process. While such pixels have generally lower chroma, their population may be overwhelming (because, for example, there may be a large number of text characters on a page). For example, a scan of a test pattern including black text and a small (e.g., four (4) point), bright colored word, may produce legitimate color pixels that represent only about 0.001% to about 0.01% of all the pixels above a reasonable chroma threshold.
The present invention provides a new and improved method and apparatus which overcomes the above-referenced problems and others.